Door destroyed, house entered, no warrant shown, dogs shot, couple bound.

CNN article

There's a few circumstances where a residence can be searched and entered without a warrant; for example, if a crime was committed near a window or otherwise can be seen from outside, if criminal evidence is in plain sight and only that evidence is obtained and the residence isn't searched, or if a suspect flees into a residence after committing a crime.

I do not know Maryland animal and police brutality law, but the dogs probably did not post a lethal or serious threat, so it's likely that the police used excessive force, and they probably used excessive force by not knocking. Furthermore, if the dogs were threatening enough to legally merit shooting them in a lawful search, I wouldn't be surprised if shooting them is illegal anyway since this search was unlawful. It could be reasonable to not knock if the marijuana recipients (read the article now if you haven't already) knew that marijuana was being mailed to them and would thus hide the marijuana when the police announce their entry. However, the couple did not know that the package contained marijuana because the distributor planned to mail it to have it intercepted before the couple received it.

I doubt there's any legal precedent to suggest that it's reasonable for these cops to think that what they were doing was legal, so official immunity shouldn't protect them.